X-ray diffraction studies of fibers and crystals of deoxygenated sickle cell hemoglobin.

Abstract

Paracrystalline fibers of deoxygenated sickle hemoglobin in erythrocytes or concentrated solutions exhibit a phase transformation to a fully crystalline state. X-ray diffraction patterns of the fiber and crystallites are similar except in two respects: the equatorial spacings of the fibers suggest that they pack into a square lattice with a = 220 A, whereas those of the crystals can be indexed on the basis of a net of 187 A by 54 A, and the second-order near-meridional reflections are strong on the fiber pattern but weak on that of the crystallites. The crystallites are isomorphous with single crystals gown in polyethylene glycol solution at pH 4.5 whose structure has been determined at near-atomic resolution (Wishner, B. C., Ward, K. B., Lattmen, E. E. & Love, W. E. (1975) J. Mol. Biol. 98, 179-194). Double filaments of molecules with an axial repeat of 64 A comprise the basic unit of both the crystal and fiber structures. Each filament of the pair is translated with respect to its neighbor by half a molecular diameter along the fiber axis. The two filaments are held together by contacts made by Val 6ft in the molecules of one strand with hydrophobic side chains of the molecule in the neighboring strand. This interaction is probably the cause of the aggregation of filaments into fibers that leads to the sickling of erythrocytes.X-ray diffraction patterns (1) of polymers found in sickled erythrocytes of individuals homozygous for sickle cell hemoglobin (Hb S) and in concentrated solutions of deoxygenated Hb S show a series of sharp meridional reflections arising from a 64-A repeat along the fiber. Potentially, these diffraction patterns contain information about intermolecular contact regions within the polymer, but, because of the poor resolution inherent in cylindrically averaged fiber diagrams and because insufficient parallel alignment of fibers further decreases the resolution, the surface lattice of the polymer has not as yet been established from these patterns; without it the intermolecular interactions cannot be determined.The packing of molecules into the polymers should be evident from electron micrographs, but these show several polymorphic forms, including a 6-stranded microtubular structure (2) and 14-stranded solid elliptical cylinders (3). Occasional sheetlike structures (4), and six-membered discs (5) have also been observed. Such a wide range of polymorphism is difficult to reconcile with our diffraction patterns, all of which appear similar except for differences in resolution. The patterns most likely arise from a single diffracting system.On re-examination of deoxygenated sickled erythrocytes sealed in capillaries several years ago, we have discovered strongly birefringent ribbonlike structures as well as bundles of needles of about 3-&,m diameter and 1-cm length. These were in equilibrium with a water clear solution, which showed that they could not be fibers because the critical equilibrium concentration of the polymer-monomer system of deoxy-Hb S is about 0.22 g-cm-3 (6) under th...

Electron microscope study of the kinetics of the fiber-to-crystal transition of sickle cell hemoglobin.

“…This helical aggregate has been described by Josephs, Edelstein, and coworkers (1, 2, 12, 13) and has been previously observed in slowly stirred solutions (11)(12)(13) This aggregate form of Hb S ranged from a loosely organized assembly of four to five individual fibers to bundles consisting of [12][13][14][15][16][17][18][19][20] individual fibers (Fig. 1).…”

Crystal Structure of Deoxy-Human Hemoglobin β6 Glu → Trp

“…Structural details of the double strand interactions have been elucidated from the refined structure of HbS at 2.05-Å resolution (5). X-ray fiber diffraction data, from both extracellular gels and sickled erythrocytes, are consistent with a similar arrangement of molecules in the crystal and fiber (6). Electron microscopy with image reconstruction has revealed that the basic HbS fiber is 210-Å thick and formed from 14 filament strands that associate as half-staggered pairs (7).…”

Structure of a crystal form of human methemoglobin indicative of fiber formation

“…There is also evidence that structural transformations may occur in the filaments making up sickle fibers as a consequence of time or other physical factors (Magdoff-Fairchild & Chiu, 1979;Kaperonis et al, 1986;Mu & Magdoff-Fairchild, 1992).…”

“…It has been noted that sickle-cell hemoglobin fibers are frequently polymorphic (Finch et al, 1973;Ohtsuki et al, 1977;Magdoff-Fairchild & Chiu, 1979;Kaperonis et al, 1986;Mu & Magdoff-Fairchild, 1992;Wang et al, 2000), which suggests that the fiber structure may be variable or ill-defined or that it consists of more than one component. There is also evidence that structural transformations may occur in the filaments making up sickle fibers as a consequence of time or other physical factors (Magdoff-Fairchild & Chiu, 1979;Kaperonis et al, 1986;Mu & Magdoff-Fairchild, 1992).…”